The present invention generally relates to liquid heating devices and, in a preferred embodiment thereof, more particularly relates to an electric water heater having a heating system providing, throughout the tank portion of the heater, equal heating wattage density for unequal volume water zones utilizing unequal wattage electric heating structures.
Conventional residential type electric water heaters are typically is provided with two electric heating elements projecting into their water storage tank portionxe2x80x94one element being mounted near the bottom of the tank, and the other element being mounted near the top of the tank. The top electrical heating element is designed to heat a small amount of water so that when the water heater is first installed, or when most of the hot water in the tank has been used, a limited amount of hot water is available. This provides at least some utility while the complete volume of tank water is heating.
Conventional commercial type electric water heaters, on the other hand, are typically provided with multiple electrical heating elementsxe2x80x94all mounted near the bottom of the tank. The theory behind this particular heating element placement is that the entire volume of water in the tank can be quickly heated using the full combined power of the multiple elements. This is a satisfactory procedure when a large volume of hot water is used. However, if only a small water draw is taken, all the elements will fire and temperature overshoot can occur as the power is being applied at a very high rate. Additionally, the full power consumption is used whether a very small amount of water or a very large amount of water is being drawn from the tank. AS is well known, this results in an undesirably high electrical load factor in low water draw situations.
As can readily be seen from the foregoing, it would be desirable to provide an electric water heater in which these heating problems, limitations and disadvantages commonly associated with electric water heaters of conventional construction are eliminated or at least substantially reduced. It is to this goal that the present Invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, liquid heating apparatus is provided which is representatively in the form of an electric water heater. The water heater has a tank adapted to hold a quantity of water to be heated, the tank having a plurality of contiguous vertical zones of unequal volumes. A vertically spaced plurality of unequal wattage electrical heating structures extends Into the tank, with each electrical heating structure serving a different one of the zones. The electrical heating structures are sized in a manner such that they provide the zones with substantially equal heating wattage densities.
Representatively, the heating structures are individually controlled, and each heating structure is an Individual electrical resistance type immersion heating element. Alternatively, each heating structure could be defined by a closely grouped plurality of individual heating elements. In a first representative embodiment of the water heater the tank zones comprise a top zone contiguous with a bottom zone and having a volume smaller than the volume of the bottom zone, and the electrical heating structures comprise a top electrical heating structure serving the top zone and having a first wattage, and a bottom electrical heating structure serving the bottom zone and having a second wattage, the ratio of the first wattage to the second wattage being substantially identical to the ratio of the volume of the top zone to the volume of the bottom zone.
In a second representative embodiment of the water heater the tank zones comprise a top zone contiguous with a bottom zone and having a volume larger than the volume of the bottom zone, and the electrical heating structures comprise a top electrical heating structure serving the top zone and having a first wattage, and a bottom electrical heating structure serving the bottom zone and having a second wattage, the ratio of the first wattage to the second wattage being substantially Identical to the ratio of the volume of the top zone to the volume of the bottom zone. In a third representative embodiment of the water heater, the tank has at least three contiguous vertical zones of unequal volumes, each being served by a different one of the unequal wattage electrical heating structures.
The equal wattage density heating system incorporated in these representative electric water heater embodiments provides them with a variety of advantages over conventionally configured electrical water heaters, such advantages Including Increased water heating efficiency, a substantial reduction in undesirable temperature overshoot, and a desirable lowering of electrical load factors.